In a four-wheeled all-terrain vehicle equipped with a belt type automatic transmission apparatus of the prior art, when the vehicle is driven by selecting the forward gear position from forward, neutral and reverse positions by means of a gear shift apparatus, speed change ratio is automatically changed by the belt type transmission apparatus according to the vehicle speed. However, when the operation depends on automatic transmission only, such troubles may be encountered as the maximum speed is restricted to a low level or, on the contrary, the speed becomes too high, and therefore it is common to provide a speed change apparatus for selecting high speed or low speed, in addition to the gear shift apparatus.
However, it is inconvenient to operate the speed change apparatus for selecting high speed or low speed and the gear shift apparatus separately. In order to overcome this problem, for example, Japanese Patent Kokai Publication No. 8-337131 discloses a speed change mechanism which allows it to shift between forward, neutral and reverse positions and select high speed or low speed by means of a single speed change lever.
This speed changing mechanism has a guide gate for guiding and positioning the speed change lever housed in a casing installed below a fuel tank cover on one side of the vehicle body. With this configuration, shift between forward, neutral and reverse positions and selection of high speed or low speed are carried out by operating the single speed change lever along the guide gate. The guide gate consists of a lateral slot and a longitudinal slot, so that the speed change lever is moved along the lateral slot when shifting between forward, neutral and reverse positions and along the longitudinal slot when changing the speed. That is, the rider moves the grip of the speed change lever along the lateral slot when selecting high speed or low speed, and along the longitudinal slot when shifting between forward, neutral and reverse positions.
Meanwhile, a four-wheeled all-terrain vehicle is generally small in size. Particularly because the rider sits astride a seat, places available for the installation of operating means except for a steering handlebar are limited. Moreover, the rider is required to quickly carry out shift changing operation while sitting astride the seat and holding the handlebar. Thus it is inconvenient to operate even a single speed change lever longitudinally and laterally , and it is also inconvenient to operate a speed change lever when the lever is installed away from the rider's hand position. Also another drawback is that the shift positions of the change lever are hard to recognize. Even with a lever operating mechanism which does not require it to operate the speed change lever laterally and longitudinally, it becomes inconvenient to operate the change lever and the speed change lever may interfere with the rider's leg, in case the location of the speed change lever exposed to the outside of the vehicle body is not proper, or in other case the speed change lever swings in a significantly large stroke.
For a speed change apparatus provided on a four-wheeled all-terrain vehicle of the prior art, there is one configuration which employs a change drum similarly to a speed change apparatus for motorcycles disclosed in the Japanese Utility Model Kokoku Publication No. 1-7883, which allows it to change the speed by operating in one direction with a simple construction. The change drum has a plurality of cam grooves formed thereon, with a pin of a shift fork for operating a shifter being engaged in each cam groove. Therefore, rotating the change drum causes the shift fork to move the shifter thereby changing the gear position.
In the case of a motorcycle, operation of such a speed change apparatus is carried out by the rider stepping on or returning a change pedal with a foot thereby to rotate the change drum, repeating the similar operation on the change pedal which has returned to an initial position by a spring force, so that the shift fork moves to attain the desired speed change ratio. Therefore, a plurality of change pedal operations are required to attain a desired speed change ratio.
In the case of a four-wheeled all-terrain vehicle equipped with a belt type automatic transmission apparatus, the change drum is rotated by operating a speed change lever installed near the rider's hand position thereby pushing and pulling a tie rod or a push-pull cable. In this case, however, operating stroke of the speed change lever must be large in order to rotate the change drum so that all the speed change ratios available are covered. It is not desirable to install a speed change lever having a long stroke on a vehicle having a narrow space around the driver's seat such as a four-wheeled all-terrain vehicle.
There is also such a problem that, in order to secure a preferable operating stroke of the speed change lever, the change drum becomes larger thereby occupying a significant portion of the inner space of the speed change apparatus. This results in an increased size of the speed change apparatus which poses another disadvantage in terms of weight.
The present invention has been accomplished to solve such problems as described above.
Accordingly, it is an object of the present invention to provide a four-wheeled all-terrain vehicle having a speed changing mechanism which allows a rider easily to change between forward, neutral and reverse positions and to select high speed or low speed by operating a single speed change lever in one direction and to easily recognize shift positions. It is another object of the present invention to provide a speed change apparatus having a light-weight, compact and simple speed changing structure suitable for four-wheeled all-terrain vehicle, which allows it to change forward, neutral and reverse position, and to select low speed and high speed by continuously operating a speed change lever over a short stroke in one direction.